Field of the invention The present invention relates to concentric camshaft arrangements and particularly to concentric camshaft

arrangements that use roller bearings to support the loads of the camshaft. The term "roller bearing" is used herein to refer to an anti-friction bearing that employs any form of rolling elements, such as balls, cylindrical rollers or needle rollers.

Background of the invention Known concentric camshafts have an inner shaft and an outer tube that are rotatable relative to one another. A first set of cams is fixed for rotation with the outer tube and a second set of cams is mounted on bearing journals on the outer tube and connected for rotation with the inner shaft by means of pins that extend through circumferentially elongated slots in the outer tube.

Such known concentric camshafts are typically supported in the engine using hydrodynamic bearings to allow the camshaft to rotate within the engine. JP2010196488 describes an example of a concentric camshaft supported in a cylinder head in this manner.

It is desirable in the automotive industry to minimise frictional losses for improved fuel consumption and reduced CO2 emissions. It is therefore attractive to use roller bearings, that exhibit lower friction, to support the loads of concentric camshafts, rather than traditional

hydrodynamic bearings. WO2012/014069 discloses the use of a roller bearing to support the loads of a camshaft. As well as offering significant benefits in term of lower friction, especially at lower engine speeds, roller bearings require very little in the way of an oil supply. Therefore, the oil pump can be reduced in size, potentially reducing losses further.

However, the use of roller bearings presents a problem in that the bearing journals supporting the movable cam lobes of the second set on the outer tube of a concentric camshaft require an oil feed to reduce friction and prevent wear between the moving cam lobes and the camshaft outer tube. If roller bearings are used to support the loads of known concentric camshafts, providing an oil feed via one or more of the hydrodynamic bearing journals of the concentric camshaft is no longer possible and an alternative oil feed is required to lubricate the journal bearings of the second set of cam lobes.

Object of the invention

It is therefore desirable in the automotive industry for there to be an improved concentric camshaft arrangement which overcomes the problems associated with known

arrangements .

Summary of the invention

According to the present invention there is provided a concentric camshaft arrangement comprising an inner shaft, an outer tube concentrically arranged around the inner shaft and rotatably supported in a cylinder head, a first set of lobes fixed for rotation with the outer tube, a second set of lobes rotatably supported by bearing journals on the outer tube and connected for rotation with the inner shaft, a roller bearing mounted between the outer tube and the cylinder head, and an oil feed for supplying oil for lubricating the bearing journals of the second set of cam lobes, wherein at least part of the oil feed is defined by a radial clearance between the outer surface of the outer tube and an inner surface of the cylinder head that is sealed at its axial ends, the radial clearance being larger than any radial clearance at the roller bearing so that loads on the camshaft are supported at least predominantly by the roller bearing .

The sealing means advantageously comprises a first and second seal ring each providing a seal between the outer surface of the outer tube and the inner surface of the cylinder head.

In one embodiment, the outer tube includes a separately formed oil feed collar fixed securely to the outer surface of the outer tube for rotation therewith, the outer surface of the oil feed collar being the surface that is spaced from the inner surface of the cylinder head by the radial

clearance forming the oil feed.

The diameter of the outer surface of the outer may be substantially equal to the outer diameter of the roller bearing . Brief description of the drawings

The invention will now be described further, by way of example, with reference to the following drawings, in which:

Figure 1 is a cross section taken through the

longitudinal axis of a concentric camshaft arrangement according to the prior art;

Figure 2 is a cross section taken through the

longitudinal axis of a concentric camshaft arrangement of a first embodiment of the present invention;

Figure 3 is a cross section taken through the

longitudinal axis of a concentric camshaft arrangement of a second embodiment of the present invention; Figure 4 is a cross section taken through the

longitudinal axis of a concentric camshaft arrangement of a third embodiment of the present invention;

Figure 5 is a cross section taken through the

longitudinal axis of a concentric camshaft arrangement of a fourth embodiment of the present invention; and

Figure 6 is an alternative cross section view through the longitudinal axis of a concentric camshaft arrangement of Figure 5.

Detailed description of the embodiments

Referring to Figure 1, a known concentric camshaft 10 has an inner shaft 12 and an outer tube 14. A first set of cams 16 is fixed for rotation with the outer tube 14 and a second set of cams 18 is rotatably mounted on bearing journals on the outer tube 14 and connected for rotation with the inner shaft 12 by means of pins 19 that pass through circumferentially elongated slots 30 in the outer tube 14.

An oil feed 20 is provided in one or more of the camshaft hydrodynamic journal bearings 22 and communicating with radial holes 24 in the outer tube 14, by way of an annular groove 26 in the journal bearing 22.

Pressurised oil is fed into the concentric camshaft arrangement 10 and flows along an oil feed path 28, defined between the inner shaft 12 and the outer tube 14, to exit through the slots 30 formed in the outer tube 14 directly under the bearing journals of the second set of cams 18.

In the description of the embodiments of the invention that now follows, like components have been allocated reference numerals with the same least significant digits, but in the 100, 200, 300 or 400 series, depending on the embodiment. In the appended claims, the most significant digit of reference numerals that refer to components found in several embodiments has been replaced by a prime ( ' ) .

Referring to Figure 2, a concentric camshaft

arrangement 100, according to a first embodiment of the present invention, comprises a concentric camshaft 110 having an inner shaft 112 and an outer tube 114. A first set of cams 116 is fixed for rotation with the outer tube 114 and a second set of cams 118 is rotatably mounted on bearing journals on the outer tube 114 and connected to the inner shaft 112, by pins 119, for rotation therewith.

The concentric camshaft 110 is co-axially arranged within a bore 122 of the cylinder head 121, such that a predefined clearance exists between the bore 122 and the external surface of the outer tube 114.

A camshaft oil feed 120 is formed in a portion, or pillow block, of the cylinder head 121. The camshaft oil feed 120 extends into a groove 126, which is formed in and extends around the circumference of the outer surface of the outer tube 114. A plurality of circumferentially spaced apart radial holes 124 extend radially inwards from the groove 126 through the wall of the outer tube 114.

The radial holes 124 extend into a tubular lubricating cavity 128 which forms an oil feed path extending axially between the outer surface of the inner shaft 112 and the inner surface of the outer tube 114. The lubricating cavity 128 extends past the pins 119.

The lubricating cavity 128 is formed by a predetermined clearance between the outer surface of the inner shaft 112 and the inner surface of the outer tube 114.

In use, pressurised oil is fed into the concentric camshaft 110 and flows through the lubrication cavity 128 to exit through pin slots 130, formed in the outer tube 114, directly under the bearing journals of the second set of cams 118. Accordingly, the interface between the inner shaft 112 and the outer tube 114 and the bearing journals of the second set of cams 118 are all adequately lubricated.

The camshaft arrangement 100 further comprises a drive flange 132 having a flange portion 134 and a tubular portion 136. The tubular portion 136 has an internal diameter to correspond to the external diameter of the outer tube 114 such that the drive flange 132 is fixed to an end portion 138 of the outer tube 114 for rotation therewith.

A portion of the cylinder head 121 is machined to provide a region of increased internal diameter 140, which serves to define two sides of a cavity for accommodating a roller bearing 142. The two other sides of the bearing cavity are defined by the outer surface of the tubular portion 136 and a radial surface of the flange portion 134. The roller bearing 142, which comprises rolling bearing elements 144 retained within a bearing housing 146, is pressed into the bearing cavity and fixed to the surface of the increased internal diameter 140.

The roller bearing elements 144 have a radial clearance which is less than the radial clearance between the bore 120 and the external surface of the outer tube 114. This ensures that all the camshaft loads are at least predominantly supported by the bearings, instead of being partially shared by the oil feed.

The concentric camshaft arrangement 100 further

comprises a first seal 148 and a second seal 150 serving to seal between the outer surface of the outer tube 114 and the bore 120 of the cylinder head portion 121. The first and second seals, 148 and 150, are ring-type or O-ring type seals which are disposed in sealing grooves formed one on each side of the oil groove 126 around the circumference of the external surface of the outer tube 114 such as to prevent undesirable escape of the oil from the clearance formed at the interface of the outer surface of the outer tube 114 and the bore 120. This ensures that the oil from the groove 126 passes into the radial holes 124. Third and fourth seals 152, 154 are disposed at

opposite ends of the lubrication cavity 128, and between the outer surface of the inner shaft 112 and the inner surface of the outer tube 114. The third and fourth seals 152, 154 are ring-type or O-ring type seals which are positioned in seal grooves formed around the circumference of the outer surface of the inner shaft 112 and maintain the oil within the lubricating cavity 128.

A second set of rolling bearings 156 is disposed around the outer tube 114 at the opposite end of the concentric camshaft 110 from the cylinder head portion 121.

The embodiment shown in Figure 3 differs from that of Figure 2 in that, instead of having an oil groove (126 in Figure 2) disposed around the circumference of the outer tube (114 in Figure 2), the second embodiment has a

separately formed oil feed collar 256 that is fixed to the outer tube 214, so as to rotate with and effectively form part of the outer tube 214. An oil groove 226 is disposed around the external circumference of the oil feed collar 256 and arranged to receive oil from an oil feed 220, disposed in a portion of the cylinder head 221. The oil groove 226 communicates with a plurality of circumferentially spaced apart radial holes 258, which extend through the wall of the oil feed collar 256. The radial holes 258 of the collar 256 are axially aligned with the radial holes 224 disposed in the outer tube 214, which, as previously described, provide oil into the lubrication cavity 228. The oil then exits the lubrication cavity 228 through pin slots 230, formed in the outer tube 214, directly under the bearing journals of the second set of cams 218.

The diameter of the cylinder head bore 220 also differs from that of the first embodiment in that it is equal to the external diameter of the bearing housing 246. This

arrangement has the advantage of reducing costs during manufacture by avoiding the need to machine a bearing cavity .

A predefined clearance exists between the bore 220 and the external surface of the collar 256. This ensures that all the camshaft loads are properly supported by the

bearings rather than being partially shared by the oil feed.

The arrangement according to the second embodiment also allows for camshaft axial thrust control. A flanged portion 260 projecting from the axial end of the oil feed collar 256 abuts an axial surface of the cylinder head 221 to limit axial displacement of the camshaft.

The oil feed collar 256 also provides a control feature 262 to control the end float of the roller bearing 242. First and second seals 248, 250 seal between the outer surface of the collar 256 and the bore 220 of the cylinder head portion 221.

The first and second seals 248, 250 are ring-type or 0- ring type seals which are disposed in seal grooves formed each side of the oil groove 226 around the circumference of the external surface of the collar 256 such as to prevent undesirable escape of oil from the clearance formed at the interface of the outer surface of the collar 256 and the bore 220. This ensures the passage of oil from the groove 226 into the radial holes 258.

Having the first and second seals 248, 250 disposed in the collar 256 eliminates the need for grooves in the outer tube 214 and therefore advantageously allows the camshaft to maintain its integral strength.

Third and fourth seals 252, 254 serve the same purpose as the seals 152 and 154 in the first embodiment.

The third embodiment of the invention, as shown in Figure 4, comprises a second oil feed 364 disposed in a portion of the cylinder head 321. The second oil feed 364 serves to provide a pressurised oil supply to a camshaft phaser oil supply cavity 366 for use with a phaser having an integral spool valve for controlling the phase of the camshaft.

A second oil groove 368 is disposed around the external circumference of the oil feed collar 356 and arranged to receive oil from the second oil feed 364. The second oil groove 368 communicates with a plurality of

circumferentially spaced apart second radial holes 370, which extend through the wall of the oil feed collar 356.

The second collar radial holes 370 are aligned with a plurality of circumferentially spaced apart second outer tube radial holes 373, which are in fluid communication with the phaser oil supply cavity 366 to provide pressurised oil from the second oil feed 364 thereto. A fifth seal 372 is disposed in a seal groove extending circumferentially around the external circumference of the collar 356, such that the second oil groove 368 is disposed between the first seal 350 and the fifth seal 372. The fifth seal 372 is, once again, a ring-type or O-ring type seal.

It will be appreciated that a greater number of oil feeds may be provided in the same camshaft arrangement to accommodate either a standard camshaft phaser, which

requires two feeds/returns, or a twin camshaft phaser, which requires four feeds/returns. Figures 5 and 6 show a fourth embodiment of a

concentric camshaft arrangement 400 having similar features to the embodiments described above. Figures 5 and 6

additionally show a hydraulic cam phaser 474 installed in the cylinder head 421. In this embodiment, instead of using two separate oil feeds, as described in relation to the third embodiment, a single oil feed 420 is used to feed oil into both the concentric camshaft 410 and the phaser 474.

As described with reference to previous embodiments, the oil feed 420 extends into a collar oil groove 426 from which a plurality of radial holes 458 extend through the collar 456 and align with radial holes 424 which extend radially through the outer tube 414. The outer tube radial holes 424 extend in fluid

communication into an oil distributor 480 which comprises a camshaft oil distributor 482 and a phaser oil distributor 484. The camshaft oil distributor 482 has a plurality of camshaft oil supply channels 486 which are in fluid

communication with lubrication cavity 428 for supplying oil thereto. As previously described, the lubrication cavity 428 supplies oil through pin slots 430 for lubrication of the bearing journals of the second set of cams 418. The phaser oil distributor 484 has a plurality of phaser oil supply channels 488 which are in fluid

communication with phaser oil supply cavities 466 to supply pressurised oil thereto.

The camshaft oil distributor 482 additional comprises a camshaft oil restrictor 490 (or alternatively this may be a small drilling) to control and balance the relative flow of oil into the camshaft and the phaser.

A one-way valve 492 can be positioned in either the feed to the phaser or camshaft to control oil flow and prevent oil drainage from the phaser when the engine is stopped .

Figure 6 provides an alternative section view showing oil feed drillings 494 for the integral spool valve 496.